The routine diagnostics and research in analytical, clinical and biochemical laboratories is often based on biochemical assay methods using different tags or labels coupled to specific reagents allowing sensitive and specific determination of desired compounds in the samples. The typical labels e.g. in immunoassays are different radioactive isotopes, enzymes, different luminescent and fluorescent molecules, for example those of chelates of rare earth metals.
The detection of the analyte can be done directly based on the label, or indirectly, as is done for example in enzymatic assays and in immunoassays. Enzyme immunoassays (ELISA) are often based on enzyme substrate molecules labelled with a reporter group, which upon enzymatic reaction is turned into light absorbing compound, i.e. its absorbance properties are changed upon enzymatic reaction in respect of absorbance wavelength or molar absorptivity. Alternatively enzyme activity can be measured using fluorogenic or luminogenic substrates which upon enzymatic reaction form highly fluorescent, or luminescent respectively, end products. Respectively enzymes as such can be quantitated in the samples using similar substrates. The enzymatic activity is subsequently monitored either kinetically or by end-point detection with a suitable photometer, fluorometer in case of fluorogenic substrates are used, or luminometer if luminogenic substrate are used.
Fluorometric detection is used in various assays based on fluorescent labels or fluorogenic substrates. Fluorometric detection with a fluorometry is based on excitation of the label by excitation light, and detection of the relaxation process of the molecule by its emission which generally takes place at a longer wavelength. In prompt photoluminescence (FI) the emission signal is measured simultaneously and/or immediately after excitation. In time-resolved fluorometry (TRF), the signal acquisition window starts after a determined delay from the excitation pulse. This way quickly decaying emission signals from other sources will have less disturbing effects. Typically TRF measurements are applied with labels with relatively long photoluminescence life-time, for example with chelates of rare earth metals having decay time in the range from microseconds to milliseconds.
A further commonly used measurement method is chemiluminescence measurement where the label is excited by a chemical reaction, and emission of the label molecule is measured from a sample without prior illumination.
A typical instrument in research, biochemistry, screening or in clinical laboratory is microtitration plate based filter photometer, fluorometer or luminometer. The instrument may also be multipurpose reader able to measure different labels, or it may be composed of monochromators.
A measurement instrument may comprise only a measurement unit for providing the optical measurement, and a control unit 70 controlling the measurement and processing detected signals. In such a case the other steps of the assay or sample pre-treatment must be performed separately. These assay steps may include sample pre-treatment, partial purification, dilution, filtrations, elution, pre-incubation with required reagents, intermediate and final washings, shakings, incubations and so on. In heterogeneous specific binding assays the added reagents which may contain excess of labels are generally washed before signal development and/or detection. If it is desired to make measurements with different measuring methods, the sample handling must be performed separately for each kind of measurement. Also, it may be necessary to use different types of measurement instruments for different measurement modes.
There are also automated analysing instruments which perform all or part of the assaying steps automatically within the instrument. Next an exemplary automated instrument is briefly discussed.
FIG. 1 illustrates an instrumentation where samples are assayed automatically. FIG. 1 shows schematically a side view of a measuring apparatus 10 and a sample dispenser 20, which is connected to it. The main parts of the measuring apparatus 10 are a shaker/incubator 30 also functioning as the store of sample plates, a reagent cassette 24 and a measurement head 50. Inside the measuring apparatus 10, there are also various sample handling devices 13-18. A conveyor 12 and an elevator 31 are used for transferring a sample plate 11.
Empty sample plates 11 are first loaded into the measuring apparatus 10. This is performed by feeding the sample plates one by one on the conveyor 12 at that end of the apparatus which is situated by the sample dispenser 20 on the left side of FIG. 1. The conveyor 12 transfers the sample plate 11 to the elevator 31 which lifts the sample plate 11 into the shaker/incubator 30. Before the actual operation of the measuring apparatus 10, reagent boxes 26 needed in the measurement must be loaded in the reagent cassette 24 of the measuring apparatus 10.
When the measuring apparatus 10 is actuated, the elevator 31 and the conveyor 12 fetch the first sample plate 11 from the shaker/incubator 30, which functions as a store of sample plates, and convey it in front of the washer 13. The valve 14 of the washer 13 dispenses washing liquid from a container outside the measuring apparatus 10 to the sample plate 11 under a pipetting apparatus 41. The pipetting apparatus 41 fetches an unused pipette tip 28 and dispenses the reagent material from a reagent bottle 45 in the reagent cassette 24 on the sample plate 11.
The sample plate 11 with the reagent material is then transferred to the shaker/incubator 30 which performs shaking and simultaneous incubation. Then the elevator 31 transfers the sample plate 11 back on to the conveyor 12 whereby the sample plate 11 is again transferred under the washer 13. After washing, the sample plate 11 is carried under a measuring liquid dispenser 17 where a pump 18 of the measuring liquid dispenser 17 dispenses measuring liquid into the wells of the sample plate 11 from a bottle 19. The sample plate 11 is then again conveyed to the shaker/incubator 30 where a shaking is performed. After shaking, the sample plate is transferred to the measurement unit 50 for measurement. After the measurement, the sample plate 11 is transferred back to the shaker/incubator 30 which functions as the store of the sample plates 11. The sample plate is finally transferred with the elevator and the conveyor to an unloading position.
Measurement instruments are increasingly used for screening purposes. One example of screening is neonatal screening in which blood spots of newborn babies are measured. The blood spots are generally impregnated into a filter paper, and small discs are punched from the filter paper as samples to be measured.
In screening applications the number of samples is large and therefore high efficiency of assaying and measurements of the samples are required. Also, it is often required to perform different kinds of assays with possibly different chemistries, and use different kinds of measurement modes in the optical measurements. The large numbers of samples need to be measured with high accuracy and reliability.
The known automated instruments are capable of processing several sample plates simultaneously. However, it is generally not possible to have different kinds of assays with possibly different chemistries simultaneously processed in those instruments. For example, a conveyor belt commonly used for transferring the sample plates can transfer only one sample plate in only one direction at a time. A sample plate is also located on the conveyor during the processing of phases of the sample plate. It is not possible to move any other sample plates during the processing of one sample plate situated on the conveyor. Also, the sample plates need to be conveyed relatively long distances inside the instrument. For example, when a certain unit has finished processing a sample plate, it takes time to transfer the processed plate to the storage and to transfer a next, unprocessed plate, to the processing unit. And during the transfer, it is not possible to utilise the processing units which are located by the conveyor. This increases the required overall processing times. Therefore the known automated instruments are practically limited to performing one type of assay successively at any time.
The different kinds of assays need different kinds of processing. For example, the phases of shaking incubation, non-shaking incubation, high temperature incubation, room temperature incubation and dispensing of different kinds of reagents need to be done in different succession in different types of assays. Therefore, it is difficult if not impossible to perform assays of different types possibly including different chemistries simultaneously in an automated instrument.
The known automated instruments do not provide all functions required for different kinds of assays. For example, different types of assays require different temperatures of wash solution. However, the automated systems generally have constant washing procedures which may not be suitable or at least optimized for all types of measurements. It is also difficult to update new functions to the known instruments because the instruments have no required space or required interfaces for additional functional units.
Further, in many screening purposes it is necessary to perform the optical measurement of samples with different measurement modes, such as prompt photoluminescence, time-resolved fluorometry, chemiluminescence and absorbance measurement modes. However, since the known automated instruments are practically limited to simultaneously performing only one type of assays, they generally also have a capability for only one mode of optical measurements.
For the above reasons it is necessary to have a multitude of equipment for efficiently measuring large numbers of samples with different kinds of assaying, chemistries and measurement modes.
There are also some other disadvantages related to the prior art instruments. The instruments must generally be in a standby state when reagent containers are filled or changed or when sample plates are loaded/unloaded. This means that the user must wait for a suitable phase in the processes of the instrument until those procedures of filling/changing/loading/unloading are possible. This also concerns the filling of a washing solution container and emptying of a waste tank of the instrument. A user thus needs to plan the work schedule according to the schedules of the instrument. And these servicing functions also tend to take much user's time and the processing time of the instrument. Preparing, transferring and handling of large containers of washing liquid and waste tanks also includes much manual work in a laboratory.
One further disadvantage of the known instruments is that they tend to require much space on the laboratory floor because of the large number of successive processing units within the instrument. This is especially a problem is several instruments are needed for performing different kinds of measurements of for achieving the required efficiency.
An automated system for effective screening must function in a reliable manner. Even short periods out of operation have a negative effect on the workflow of a laboratory. As various types of samples and other liquids are transferred through tubes, valves and nozzles, there may appear clots which prevent the normal operation of the system.
An automated system for effective screening must provide accurate and reliable measurement results for each measurement even when the rate of measurements is high and when the types of measurements vary between samples. If known instruments could be modified for measuring more effectively a larger number of different kinds of samples, it could be difficult to maintain the required accuracy and reproducibility of the measurements. This concerns, for example, achieving the required accuracy and reproducibility in dispensing volumes and dispensing positions of reagents.